In radiographic technology, X-ray imaging systems using solid-state image pickup elements in place of X-ray sensitive films have come to be widely used in recent years. Such X-ray imaging systems are more convenient such as allowing confirming X-ray images in real time without the necessity for development as in X-ray sensitive films, and have a point of superiority also in the aspect of the storage stability of data and ease in handling. For example, also in X-ray photography for dental diagnosis, such X-ray imaging systems have spread in various imaging modes such as panoramic mode, cephalometric mode, and CT. As an example, a dental X-ray apparatus disclosed in Patent Document 1 images X-rays having been output from an X-ray source and transmitted through a subject, by an X-ray detecting element of a CCD type.
Moreover, as solid-state image pickup devices to be used for such X-ray imaging systems, ones using CMOS technology are known, and among these, a passive pixel sensor (PPS) type device is known. The PPS type solid-state image pickup device includes a pixel array where PPS type pixels including photodiodes for generating charges of amounts according to incident light intensities are two-dimensionally arranged in M rows and N columns, converts a charge generated in the photodiode in response to light incidence in each pixel to a voltage value in an integration circuit, and further converts this voltage value to a digital value to be output.
Generally, an output terminal of each of the M pixels of each column is connected, via a readout wiring line provided corresponding to the column, with an input terminal of an integration circuit provided corresponding to the column. And, charges generated in the photodiodes of the respective pixels are, in sequence from the first row to the M-th row and row by row, input to the integration circuit through the readout wiring line corresponding to the column, and a voltage value according to the charge amount is input from the integration circuit to an analog/digital converter in sequence from the first column to the N-th column.